A pair of tubes can be joined by inserting the end of one tube into the end of the other in a telescoping fashion, and forcing an internally tapered lockring over the telescoped tube ends. Earlier U.S. Pat. Nos. 3,827,727 and 4,026,006 describe lockrings which are internally tapered for radially compressing the outermost tube to squeeze it tightly against the innermost tube. A large radial force results at the rear end of the taper where the lockring has its smallest internal diameter. While such lockrings can reliably join a pair of tubes, additional improvements are desirable.
A relatively large installation force, such as about 500 lbs., is required to push such a lockring over the tubes, to install a ring over 1/2 inch (external diameter) aluminum tubing. Where thinner wall tubing is used, a lower installation force would be desirable to avoid the possibility of buckling of the tubes. The elasticity of the tube joint, which is its strength when subjected to large changes in temperature (and consequent expansion or contraction) or when subject to loads, depends on the radial elasticity of the installed lockring and the proportion of the length of the lockring where it elastically squeezes the tubes together. A lockring and joint which enabled lower installation forces for the lockring while providing elastic compression of the tubes along a cylindrical portion of a considerable length of the ring would be of great value.